10 g 



EVOLUTION OF COLOR PATTERN IN LITHOCOLLETIS. 107 



In all, the larva is of the so-called cyhndrical type, which agrees well with the 

 usual type of lepidopterous larva. During the first three instars, in which the 

 extent of the mine is gradually increased by a loosening of one epidermis, the 

 larva has a characteristicahy flattened shape, with flat 

 head and projecting mouth-parts. After the third moult, 

 the larva assumes the normal cylindrical shape and the 

 mine becomes tent-hke by a fold in the loosened epider- ^S^TITb'^ 

 mis. The larva then consumes the greater part of the ^S^S^^fc=^ 

 parenchyma within the area occupied by the mine. The 

 pupa, except that of one species, is always formed within maMoinhydT 

 the mine and may or may not be enclosed in a cocoon. 



The forewings of the imagoes are marked by various combinations of white 

 transverse fascise and streaks on a yellowish ground color. These white marks 

 are bordered along their inner edges by dark brown or blackish scales; some- 

 times, but to a less extent, dark scales may also appear along their outer edges. 

 The hindwings are unicolorous. 



Our American species while conforming in all structural characteristics to 

 those of Europe, fall naturally into two groups; one of these agrees closely in 

 structure of larva and imaginal markings with the European type just described; 

 the other has what has been termed the ^^flat larva,'' and the imagoes produced 

 from such larvae can always be sharply distinguished by their markings from the 

 species of the ''cylindrical-larval group.'' The ''flat larva" retains the flat 

 shape, which is characteristic of the first three instars of the "cylindrical-larval 

 group," through the fourth, fifth and sixth instars, only assuming the cylindrical 

 shape and an approach to normal mouth-parts with the last moult. By some 

 systematists, the persistence through three additional larval instars of the curious 

 modification of the mouth-parts, which is in fact an adaptation for loosening 

 the epidermis, has been regarded as a sufficient ground for the generic separation 

 of this group, and the name Cameraria Chapman has been applied to it (Chap- 

 man, '02). The other view, which regards the modification of the mouth-parts 

 merely as an adaptation for a particular mode of life, and not a character indi- 

 cating the natural separation of that group from one with which the imagoes 

 agree in all structural details, has been presented in the Canadian Entomologist 

 for December, 1909 (Braun, '09). 



The mines of the "flat-larval group" are alwa^/^s found upon the upper side 

 of the leaf. The increase in the extent of the mine continues through six instars, 

 the larva consuming only a few layers of cehs in front of it. For this reason, 

 the parenchyma within the mine is never entirely consumed and the mine 

 rendered semitransparent, as is the case in mines of the " cyhndrical-larval 

 group." During the seventh instar, the larva does not feed; the time is occupied 

 in preparation for the pupal state. Where the imago is to emerge the same 

 summer, most of the species spin cocoons. The cocoon is a flat, oval sheet of silk 

 attached around its edge to the floor of the mine, the epidermis above being 



